While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. Deep-UV lithography is capable of achieving a minimum feature size of 0.5 μm or less and, when a resist having low light absorption is used, can form patterns with sidewalls that are nearly perpendicular to the substrate.
Recently developed acid-catalyzed chemical amplification positive resists, such as those described in JP-B 2-27660, JP-A 63-27829, U.S. Pat. Nos. 4,491,628 and 5,310,619, utilize a high-intensity KrF excimer laser as the deep-UV light source. These resists, with their excellent properties such as high sensitivity, high resolution, and good dry etching resistance, are especially promising for deep-UV lithography.
Such chemically amplified positive resists include two-component systems comprising a base resin and a photoacid generator, and three-component systems comprising a base resin, a photoacid generator, and a dissolution inhibitor having acid labile groups.
For example, JP-A 62-115440 describes a resist material comprising poly-4-tert-butoxystyrene and a photoacid generator, and JP-A 3-223858 describes a similar two-component resist material comprising a resin bearing tert-butoxy groups within the molecule, in combination with a photoacid generator. JP-A 4-211258 describes a two-component resist material which is comprised of polyhydroxystyrene bearing methyl, isopropyl, tert-butyl, tetrahydropyranyl, and trimethylsilyl groups, together with a photoacid generator.
JP-A 6-100488 discloses a resist material comprised of a polydihydroxystyrene derivative, such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxycarbonyloxy)styrene] or poly[3,5-bis(2-tetrahydropyranyloxy)styrene], and a photoacid generator.
The base resins in these resist materials have an optimum baking temperature as high as about 130° C. when the acid labile group is tert-butyl, and low resolution when the acid labile group is tert-butoxycarbonyl. In either case, the resist pattern tends to take on a T-top profile. By contrast, when the acid labile groups are alkoxyalkyl groups such as ethoxyethyl which are cleaved by weak acids, the corresponding resins have the drawback that the pattern configuration is considerably narrowed with the passage of time between exposure and heat treatment. This makes it difficult to form a resist film to a reduced thickness compliant with a reduced feature size. Moreover, the presence of bulky groups on the side chains lowers the heat resistance of the resin and leads to an unsatisfactory sensitivity and resolution. These problems have hitherto prevented the practical implementation of either approach, and workable solutions have been sought.
To provide higher transparency and firm adhesion to substrates and to improve footing on substrates and etching resistance, JP-A 3-275149 and 6-289608 propose resist materials using copolymers of hydroxystyrene with a tertiary ester of (meth)acrylic acid. The resist materials of this type suffer from poor heat resistance and an indefinite pattern profile after exposure and are not satisfactory in resolution as well.
With the current trend toward higher resolution, thinning of pattern film is in simultaneous progress. Accordingly, there is a desire to have a resist material having higher etching resistance.